Recently, a system has been in widespread use in which a vehicle is equipped with a detecting device that detects various kinds of information in order to detect the congestion state of a road by collecting traffic information, and the information is then fed back to a GPS navigation device of a vehicle. For example, Patent Literature 1 discloses a technique of dividing a map in a mesh form, detecting whether a vehicle has entered or left a region of each mesh through an on-board unit, transmitting the detected information to a center server device, and analyzing the degree of congestion based on the number of vehicles located in a mesh.